1. Field of the Invention
This invention relates to a memory cell, which is formed on a semiconductor substrate constituted of silicon, or the like. This invention also relates to a method of inputting and outputting information.
2. Description of the Prior Art
With the increased use of the Internet in recent years, there has arisen a strong demand for computers, particularly personal computers (hereinbelow referred to as the "PC"), and rapid advances have been made in the related techniques. Also, the market requires products, which have as high a performance as possible and are as cheap as possible, and research has continuously been carried out in order to satisfy the requirements of the market.
One of important factors for determining the performance of computers is a storage device. Currently popular storage devices are semiconductor storage devices, which comprise a semiconductor substrate constituted of silicon, or the like, and memory cells formed on the semiconductor substrate. In order for a storage device to have a high performance, the storage device should primarily satisfy the requirements in that the inputting and the outputting of information can be carried out quickly, in that the memory should have a large capacity, and in that the stored information can be retained with a high stability. It will be possible for computers to take constitutions in accordance with various requirements of the market. However, if both of the requirements for the quick operation and the large capacity are to be satisfied, the cost cannot be kept low. The cost can be kept low by compromising on either one of the two requirements.
In the currently most popular main body memories of PC's, cache memories and main memories are constituted of random access memories (RAM's). As the RAM's, dynamic random access memories (DRAM's) and static random access memories (SRAM's) are used.
The DRAM's have a larger capacity per unit area than SRAM's and can be produced at a low cost. However, the DRAM's have the drawbacks in that, since the takeout of stored information is carried out by the discharging of electric charges, a long time is required to output the stored information, and electric charges must always be supplied (refreshed). With the SRAM's, the takeout of stored information is carried out by the discrimination of the state of a multivibrator. Therefore, with the SRAM's, refreshing operations need not be carried out, and the stored information can be read quickly. However, the SRAM's have the drawbacks in that, due to their complicated structures, the capacity per unit area is smaller than in the DRAM's, and the cost cannot be kept low.
Accordingly, in an ordinary constitution of PC memories, the SRAM's are employed as the cache memories, the DRAM's are employed as the main memories, and the cost is thereby restricted.
Also, with the DRAM's and the SRAM's, the stored information is lost when the electric power source is turned off, and therefore necessary information must be stored on other storage devices, such as disks. Memories, which have the characteristics such that the stored information may not be lost when the electric power source is turned off, include flash memories. However, due to the necessity of a high voltage for the information inputting operation, a limitation on the capacity, and the cost, the flash memories cannot sufficiently satisfy the aforesaid requirements of the current market.